In the production of a seamless metal pipe by means of a Mannesmann process, a billet or bloom heated is made into a hollow blank with use of piercing mill, and then the hollow blank is finished into a mother pipe by means of a continuance mill. When the hollow blank is rolled by the continuance mill, a mandrel bar is inserted into the heated hollow blank, then the hollow blank is continuously rolled by adjusting a gap of grooved rolls of the mill and the mandrel bar. At the step of elongation, various lubricants are used in order to reduce the friction and to prevent seizing between mandrel bar and the hollow blank.
In such hot forming under high temperature, lamellar solid lubricants such as graphite, boron nitride, and mica are usually used. Also, many proposals are provided that such lubricants are used to apply to tool in order to form a coating. According to these proposals, such lubricants provided are certainly water resistant, not peeled or washed by roll cooling water, and having almost no problem in lubricity.
However, lubricants which adhere to the spray booth, the neighboring equipments, and conveyor for transporting mandrel bar obtain water resistance when it is dried. When the dried lubricant is deposited, it is difficult to clean such areas, thus the dried lubricant worsens the working conditions. Further, lubricant deposited on equipments makes the maintenance operation of the equipments difficult; moreover it may result in malfunction and damage of such equipments.
In order to solve such inconvenience, for example, Patent Document 1 and Patent Document 2 propose lubricant compositions using water-soluble polymer. In addition, Patent Document 3 proposes lubricant composition which does not use polymer. These lubricant compositions are easily washed by water even after drying.    Patent Document 1: Japanese Patent Application Examined No. 62-34358    Patent Document 2: Japanese Patent Application No. 56-147297 (JP-A No. 58-047097)    Patent Document 3: Japanese Patent Application Laid-Open No. 8-325584